Problem: A sound wave travels through iron at a rate of $5120\,\dfrac{\text{m}}{\text{s}}$. At what rate does the sound wave travel in $\dfrac{\text{km}}{\text{h}}$ ?
Solution: We will convert $5120\,\dfrac{\text{m}}{\text{s}}$ to a rate in $\dfrac{\text{km}}{\text{h}}$ using the following conversion rates: There are $1000\text{ m}$ per $1\text{ km}$. There is $1\text{ h}$ per $3600\text{ s}$. $\begin{aligned} &\phantom{=}\dfrac{5120\text{ m}}{1\text{ s}} \cdot \dfrac{1\text{ km}}{1000\text{ m}} \cdot \dfrac{3600\text{ s}}{1\text{ h}} \\\\ &=\dfrac{5120\cdot 1\cdot 3600 \cdot \cancel{\text{m}} \cdot \text{km} \cdot \cancel{\text{s}}}{1 \cdot 1000\cdot 1 \cdot \cancel{\text{s}} \cdot \cancel{\text{m}} \cdot \text{h}} \\\\ &=\dfrac{18{,}432{,}000}{1000}\,\dfrac{\text{km}}{\text{h}} \\\\ &=18{,}432\,\dfrac{\text{km}}{\text{h}} \end{aligned}$ In conclusion, the rate in $\dfrac{\text{km}}{\text{h}}$ at which the sound wave travels through iron is: $18{,}432\,\dfrac{\text{km}}{\text{h}}$